Chromatography is a useful means of analysis which has found extensive utility in a variety of fields. It is classified broadly into several groups such as, for example, gas chromatography, column chromatography, thin-layer chromatography (TLC), and paper chromatography. TLC can further be classified into two major sub-groups, i.e., ordinary TLC using a plate having a stationary phase superposed in the form of a thin layer on a quartz glass plate, and TLC using a thin-layer rod having a stationary phase baked on a quartz glass rod. The present invention relates to a thin-layer rod for use in the TLC in the latter sub-group.
Chromatography is a method for separating a given sample into its components, detecting the components, and determining their amounts by utilizing differences the components exhibit in terms of the ratio, R.sub.f, between the speed of movement of the component of interest and the speed of movement of the developer which is fixed by the ratio of the affinity a given component shows for the stationary phase to the affinity for the developer. The differences in R.sub.f, therefore, enable separation of the components to be easily and sufficiently effected, based on the differences in affinity the components exhibit for the stationary phase. For the separation to be advantageously effected, the simple fact that the differences in affinity exist and that those differences in R.sub.f are large is not necessarily sufficient. The fact that the image of the chromatogram is not obscure but is clear and free from diffusion constitutes itself an essential requirement. If the image is obscure, the individual images of the components separated somewhat due to the differences in affinity still tend to overlap, barring the achievement of effective separation, detection, and determination of the components aimed at by the chromatography.
As one means of clarifying the differences in affinity of the components for the stationary phase and preventing the image of the chromatogram from being obscure, in the field of the column chromatography and the ordinary TLC using a thin-layer plate, the technique of chemically modifying the stationary phase by the treatment with a varying chemical substance has been utilized, as disclosed in U.S. Pats. Nos. 4,295,968 and 4,372,850.
In the ordinary TLC using a thin-layer plate, it is normal to effect the detection of the components and the determination of their amounts through measurement of the amounts of ultraviolet light absorbed by the components. This method may be suitable for qualitative analysis, but is not satisfactory for quantitative analysis. This is because the components of a given sample have different degrees of absorbance for the ultraviolet light, and, therefore, two equal degrees of absorbance exhibited by two components do not immediately mean that the concentrations of these two components are equal and, by the same token, the areas the components occupy in the chromatogram do not permit direct determination of the amounts of the components.
In contrast, the TLC conducted by the use of a flame ionization detector (FID) has the advantage that in the analysis of hydrocarbons, the areas occupied by the components in the chromatogram are available for direct determination of the amounts of the components because the responses of the detector are faithfully proportionate to the concentrations of the components by weight. It has been ascertained that even in the separation of higher hydrocarbons, the responses of the detector are faithfully proportionate to the weight concentrations. For the quantitative analysis of higher hydrocarbons, therefore, the thin-layer chromatography conducted by the use of a flame ionization detector (FID-TLC) proves to be a highly advantageous means. Unfortunately, the FID permits use of a thin-layer rod, but not the ordinary thin-layer plate, because of the restrictions imposed by the physical structure of the FID. Conventional thin-layer rods have not been chemically modified. Only thin-layer rods of a type having silica gel or alumina simply baked onto a quartz glass rod have been known to the art. These thin-layer rods are not very satisfactory in terms of the separating property, particularly because they have the disadvantage that the images of the chromatogram are subject to the phenomenon of tailing and lose clarity. Thus, they have not been fully suitable for the separation of higher hydrocarbons such as polycyclic aromatic hydrocarbons.